Lyocell fibers and methods of producing the same

The present invention relates to regenerated fibers and methods of methods of manufacturing the same. In particular the present invention relates to colored lyocell type fibers and to methods of producing the same from cellulosic raw-material.

The world's population is expected to exceed 8 billion by 2025. With an increase of the population, the global demand for limited resources has grown accordingly. Textiles are one of those resources. In 2017, the world produced a total amount of 103 million tons of fibers; of which man-made fibers accounted for 69% (72 million tons).

At the same time, textile waste has increased significantly because of the continued consumption of textile products. Studies show that the textile and apparel industries are the second largest source of pollution on the planet after the oil and mining industries. The natural resources consumed by the textile industry are mainly materials and energy used for farming, processing, manufacturing, and transportation.

Today, most post-consumer textiles are ultimately disposed of in landfills; therefore, it is necessary to develop an effective textile recycling technology to achieve a more sustainable development of the textile industry.

If recycled and converted to new fibers or yarns, colored textile waste needs to be bleached before it is further processed and respun. After recycling, the new fibers and yarns are re-dyed. This creates an additional waste stream resulting from pretreatment chemicals and dyes

The dyeing process is very important for the sale of textile products, but the dyeing of textiles has a big impact on the environment. The use of synthetic dyes consumes large amounts of chemicals, water, and energy, and emits large amounts of sewage and air pollutants. More than 50% of the production of colorants (about 1 million tons per year) are used in textile dyeing in the world. In developed countries, the dyeing and printing of one ton of fiber consumes 100 tons of water, while, in other parts of the world, it can increase to 300 or even 400 tons. Usually, wastewater discharged from the dyeing process contains relevant dyes, dispersants, mordants and surfactants (usually “unspecified” compounds present in commercial dyes), and most plants discharge untreated wastewater directly into local rivers, which negatively affects the environment.

Some of the compounds that are not readily biodegradable, such as color brighteners, softeners, and sizing agents, have a direct impact on human health and on the environment. Non-aromatic dyes often carry harmful heavy metals and therefore require a variety of toxic finishing processes.

As an alternative to the traditional wet dyeing technology, spun-dyeing provides not only excellent fiber quality, but also dyes evenly and reduces the environmental impact. In addition, it has its own unique advantages, such as bright color and luster, and excellent color fastness. Spun-dyed fibers have been shown to cause a lower environmental impact in all LCA categories than traditional dyed fabrics, including acidification, eutrophication, and ozone depletion. Moreover, with the increasing scarcity of water resources, the treatment of dye waste water is subject to stricter environmental control. The spinning and dyeing technology reduces water consumption where the fiber can be dyed with very little water.

Spun-dyed fibers are dyed during the spinning process by either dyeing the pulp, or the spinning dope.

The most critical consideration in the dyeing process is whether the polymer colorant mixture has physical and chemical stability. Especially for the dyeing of regenerated cellulose, a strong reducing agent and/or an oxidizing agent usually used in the treatment of these celluloses impairs the stability of the coloring agent.

Regarding their chemical nature, dyes can be divided into different classes such as vat dyes and reactive dyes. Vat dyes are a class of dyes that are classified as such because of the method by which they are applied. Vat dyeing is a process that refers to dyeing that takes place in a bucket or vat. The original vat dye is indigo, once obtained only from plants but now often produced synthetically. Vat dyes, which are suitable for cellulosic fiber fabrics, are resistant to light, have good washing fastness, and are resistant to chlorine bleaching and other oxidative bleaching. For example, an anthraquinone dye has been dispersed in a spinning dope as a pigment to form a recycled substrate the matrix formed is treated with a reagent to reduce the vat dye in the fiber.

In all of these techniques, reduction of the vat dye to its parent form is typically accomplished by treating the matrix with a reducing agent. However, vat dyes have some limitations because they tend to prematurely oxidize, which tends to result in uneven distribution of the dye in the spinning dope. Reactive dyes are the most used in cellulosic fiber fabrics. They are characterized by having bright color, are resistant to light, can withstand water washing and have good rubbing fastness.

At present, reactive dyes account for about 30% of global synthetic dyes. In a reactive dye, a chromophore (an atom or group whose presence is responsible for the colour of a compound) contains a substituent that reacts with the substrate. Reactive dyes have good fastness properties owing to the covalent bonding that occurs during dyeing. Reactive dyes are most commonly used in dyeing of cellulose like cotton or flax, but also wool is dyeable with reactive dyes. Reactive dyeing is the most important method for the coloration of cellulosic fibres. Reactive dyes have a low utilization degree compared to other types of dyestuff, since the functional group also bonds to water, creating hydrolysis. Reactive dyes have various chemical structures, such as azo, anthraquinone, phthalocyanine, methylazine, triazine and oxazine. Most reactive dyes are highly soluble and do not degrade in water.

[DBNH][OAc], a superbase based ionic liquid, enables the conversion of waste material from various sources such as cardboard, newsprint, and uncolored post-consumer cotton to new lyocell type fibers.

Due to their high thermal and chemical stability, ionic liquids have also been proposed as “green solvents” for various applications.

It is an aim of the present invention to provide novel regenerated cellulosic fibers, in particular from recycled cellulosic raw-material.

It is another aim of the present invention to provide a method of producing colored regenerated fibers, in particular lyocell fibers.

It is a third aim of the present invention to provide a novel method of recycling dyes, such as dyes used for coloring of fibrous matter.

The present invention is based on the finding that ionic liquids are suitable for the use in the recycling of colored textile waste, in particular of cellulosic textile waste.

The method of producing colored lyocell type fibers, typically comprises the steps of

The invention further provides for the simultaneous recycling of cellulose fibers and dyes from dyed cellulosic waste, such as cotton or flax waste, in the form of dyed lyocell fibers.

More specifically, the present invention is mainly characterized by what is stated in the characterizing portions of the independent claims.

Considerable advantages are obtained by the present invention. As will appear, the ionic liquids will have an enhancing effect in textile dyeing and can be readily applied in dry jet wet spinning processes, thus allowing for the use in the recycling of colored textile waste.

Compared to conventional dyeing procedures, the spun fibers show a better color fastness and a more even distribution of the dye within the fiber matrix. This enhances the durability and optical properties

The process will facilitate the valorization of textile waste by the creation of a circular economy, and the reduction of the carbon footprint.

The present fibers are high performance fibers with excellent tensile strength

At the same time, the present invention will reduce waste pollution caused by textile waste, as well as to lower the environmental pollution caused by textile dyeing industry. Thus, the present invention provides for simultaneous recycling of cellulose fibers and dyes from dyed cotton waste in the form of dyed lyocell fibers.

Thus, in one aspect, the present invention provides for recycling of dyes used for dyeing of cotton by dissolution of fibrous cotton matter containing said dye into an organic liquid capable of dissolving the fibrous matter and the dye to form a dope and using the dope to make new colored fibers (regenerated fibers) by spinning.

Next, embodiments will be studied in more detail with the reference to the appended drawings.

In the present context, “lyocell type fibers” and “lyocell fibers” are used synonymously. The terms stand for fibers composed of cellulose precipitated (i.e. regenerated) from an organic solution in which no substitution of the hydroxyl groups takes place and no chemical intermediates are formed.

In one particular embodiment, the present lyocell fibers are produced by dissolving the cellulose raw-material in an ionic liquid, such as an ionic liquid of the superbase type.

Superbases that can form the basis for superbase-based ionic liquids include, e.g. 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), N,N,N,N,NN-hexamethylphosphorimide triamide (HMPI), N,N,N,N-tetramethylguanidinium (TMG), and 1,2-dimethyl-1,1,4,5,6-tetrahydropyrimidine (DMP). Superbase-based ionic liquids are suitable ionic liquids in some embodiments. Ionic liquids used in embodiments are typically in the form of acid-superbase conjugates, in particular acetates such as DBUH OAC, preferably DBNH OAc, suitably mTBDH OAc are suitable ionic liquids in further embodiments

As a particular example of a superbase-based ionic liquid DBNH OAc may be mentioned. It is employed as a new generation ionic liquid in the Ioncell-F process (Sixta et al. 2014). It is able to selectively dissolve the cellulosic component, such as cotton.

In one embodiment, the present textiles comprise respun, colored lyocell type fibers. In particular, the present fibers comprise colored lyocell type fibers comprising recycled colored fibers.

In one embodiment, the fibers comprise dry jet wet spun fibers. The “dry jet wet spinning”, refers to a combination of both wet and dry spinning techniques for fiber formation. Typically, in the dry-jet-wet spinning process, high orientation is accomplished.

The novel fibers contain dye typically in a concentration of about 0.1 to 5%, for example up to 2%, by weight of the dry fibrous matter.

In one embodiment, the fibers are colored by using a colorant having a chemical structures of the azo, anthraquinone, phthalocyanine, methylazine, triazine or oxazine type.

As examples of dyes the following can be mentioned: vat dyes, in particular an Indanthren dye, or reactive dye, such as a Remazol and Levafix dye and combinations thereof.

In one particular embodiment, the dye is selected from the group of Indanthren Br Green, Indanthren Red, Levafix BrRed E-4BA, Levafix Blue E-GRN, Remazol Black 133% and Remazol Br Blue and combinations thereof.

In one embodiment, the dye is selected from the group of Indanthren Br Green, Indanthren Red, Levafix Blue E-GRN, Remazol Black 133% and Remazol Br Blue and combinations thereof. As will appear from the examples discussed below, the mechanical properties of the fibers are after spinning good.

In one embodiment, the fibers are spun from a dope comprising an ionic liquid, in particular a superbase-based ionic liquid, such as [DBNH][OAc] or [MTBDH][OAc], [DBNH][OAc] being particularly preferred.

One embodiment for producing the present novel regenerated fibers, more specifically colored lyocell type fibers, comprises generally the steps of

The raw-material typically comprises recycled cellulosic or cellulose rich textile fibers, in particular cotton fibers, such as cotton fiber waste or cotton fiber rich waste. Also other suitable cellulosic fibers, such as flax, can be used as raw-material.

The raw-material typically comprises at least 50 wt-%, preferably at least 60 wt-%, for example 75 to 100 wt-% of cellulosic fibers, such as cotton fibers. The raw-material can also contain other textile fibers, such as polyester and viscose, such as rayon, fibers. Thus, in one embodiment, the raw-material comprises colored textile fibers formed by blends of cotton and one or more of polyester, viscose and lyocell fibers and mixtures thereof.

In one embodiment, the raw-material comprises pre-consumer or post-consumer textile waste, in particular post-consumer textile waste. The textile waste can comprise materials in the form of yearn, thread, cloths, sheaths, clothes, linen and sheaths and other articles comprising fibrous matter.

One embodiment comprises the steps of

The spinning dope is typically subjected to dry jet-wet spinning to form textile fibers having a color generally corresponding to the preselected color.

In one embodiment, the regenerated fibers are spun using a spinneret (200 holes with 0.1 mm diameter).

As will appear from the below experimental data, the color of the recycled fibers will generally be preserved during the processing, although some fading may take place. Thus, the expression corresponding to a preselected color is to be understood to stand for a color of the respun fibers which is basically the same as that of the raw-material fiber but in which the intensity of the color can be somewhat lessened.

In one embodiment, which can be combined with any of the above embodiments, the textile waste to be respun has a viscosity of about 450 ml/g.